The present invention relates to a tool joint employing threaded coupling to be used in particular in cutting tool assemblies employing different heads that are used on a single tool holder.
Tool joints with male and female members employing threaded coupling are known in the art. Such a male member usually comprises an external thread portion that matches a corresponding internal thread portion in the female member. An example of such a tool joint coupling mechanism is disclosed in U.S. Pat. No. 5,114,286. As shown in ""286, a male coupler (11) is axially aligned with a female coupler (13). The male coupler (11) has a helical male thread (21) which is sized and shaped to match a corresponding helical female thread (23) in the female coupler (13). A disadvantage of the coupling mechanism of the kind described is shown schematically in FIG. 1 (and shown clearly in FIGS. 1 and 5 of ""286). It involves the fact that forward to the forward most thread crest 14 of the male member 12 there is formed a narrow neck portion 16 which weakens the forward end of the male member. The term xe2x80x9cnarrow neck portionxe2x80x9d refers, herein, to a section of the male member having a diameter equal to the root diameter of the thread.
Another problem involved with such tool joints relates to the fact that the forward most thread crest, and, also the rear most thread crest, are incomplete, having narrowing runout portions at their open ends. This is clearly shown, for example, in FIG. 2 of U.S. Pat. No. 1,407,335 to Reynolds. Such narrow end portions are too weak to transfer axial loads between the male and female members.
A solution to the problem is disclosed in U.S. Pat. No. 4,735,537 to Rath, which teaches how to reduce the narrow neck portion. In the threaded portion of the male member of ""537, the inner end portion of the thread has its full dimension almost to the point where it terminates. This enables the transition section to be made shorter.
It is the object of the present invention to provide a tool joint with male and female members having matching threads in which the threads in both the male member and the female member do not have the conventional runout of incomplete cross-section, thereby providing a shorter and stronger tool joint.
In accordance with the present invention there is provided a tool joint having an axis A and comprising a male member and a female member;
the male member having an axis B and comprising:
a male body portion; and
a male coupling portion projecting rearwardly from the male body portion, the male coupling portion having an unthreaded forward portion adjacent the male body portion and a rear threaded portion terminating at a rear end;
the threaded portion of the male coupling portion having a thread terminating in a forward end part adjacent the forward portion of the male coupling portion and in a rear end part adjacent the rear end of the rear portion of the male coupling portion, the thread having an intermediate section of uniform depth between the forward and rear end parts;
the forward end part of the thread of the male coupling portion being a thread root having a variable depth gradually decreasing from a depth equal to the uniform depth of the thread to no depth;
the rear end part of the thread of the male coupling portion being a thread crest having a variable height gradually decreasing from a height equal to the uniform depth of the thread to no height;
the female member having an axis C and comprising:
a female body portion; and
a female coupling portion comprising a bore for accepting the male coupling portion, the bore extending rearwardly from a front surface of the female member towards the female body portion, the bore having an unthreaded forward portion adjacent the front surface and a rear threaded portion terminating adjacent the female body portion;
the threaded portion of the female coupling portion having a thread terminating in a forward end part adjacent the unthreaded forward portion of the female coupling portion and in a rear end part adjacent the female body portion, the thread of the female coupling portion having an intermediate section between the forward and rear end parts, the thread of the female coupling portion having a depth equal to the uniform depth;
the forward end part of the thread of the female coupling portion being a thread crest having a variable height gradually decreasing from a height equal to the uniform depth to no height;
the rear end part of the thread of the female coupling portion being a thread root having a variable depth decreasing from a depth equal to the uniform depth of the thread to no depth;
wherein, upon threaded coupling of the male and female members to form a tool joint connection, the threaded portion of the male member engages the threaded portion of the female member;
the forward end part of the thread of the male coupling portion and the forward end part of the thread of the female coupling portion have a gap between them of a first angular extent; and
the rear end part of the thread of the male coupling portion and the rear end part of the thread of the female coupling portion have a gap between them of a second angular extent.
In accordance with a preferred embodiment of the present invention, the male body portion further comprises a rearwardly facing annular shoulder adjacent the unthreaded forward portion of the male coupling member and the front surface of the female member is a forwardly facing annular shoulder; and
wherein, upon threaded coupling of the male and female members to form a tool joint connection, the annular shoulder of the male body portion abuts the annular shoulder of the female body portion.
Further in accordance with a preferred embodiment of the present invention, the unthreaded forward portion of the male coupling portion is frustoconical in shape, rearwardly tapering towards the rear threaded portion of the male coupling portion and the unthreaded forward portion of the bore of the female coupling portion is frustoconical in shape, rearwardly tapering towards the female body portion; and
wherein, upon threaded coupling of the male and female members to form a tool joint connection, the unthreaded forward portion of the male coupling portion abuts the unthreaded forward portion of the female coupling portion.
Typically, the first angular extent is in the range of 20xc2x0 to 90xc2x0.
Preferably, the first angular extent is 70xc2x0.
Typically, the second angular extent is in the range of 20xc2x0 to 90xc2x0.
Preferably, the second angular extent is 70xc2x0.
In accordance with the present invention, the forward and rear end parts of the male and female threaded portions each have an angular extent in the range of 5xc2x0 to 30xc2x0.
Preferably, the forward and rear end parts of the male and female threaded portions each have an angular extent of 15xc2x0.
Typically, the male member is made of cemented carbide and the female member is made of steel.
In accordance with the present invention, during the threaded coupling of the male and female members the unthreaded forward portion of the male coupling member abuts the unthreaded forward portion of the female coupling member before the annular shoulder of the male body portion abuts the annular shoulder of the female body portion.
Preferably, when the unthreaded forward portion of the male coupling portion comes into initial contact with the unthreaded forward portion of the female coupling portion the annular shoulder of the male body portion is spaced a distance L from the annular shoulder of the female body portion.
Typically, the distance L lies in the range of 0.1 to 0.6 mm.
In accordance with a preferred embodiment of the present invention, the distance L equals to 0.3 mm.
In accordance with a preferred embodiment of the present invention, the annular shoulder of the male body portion and the annular shoulder of the female body portion are perpendicular to the axis A.
Typically, the annular shoulder of the male body portion and the annular shoulder of the female body portion are ground.
Further typically, the unthreaded forward portion of the male coupling portion and the unthreaded forward portion of the female coupling portion are ground.
Still further typically, the thread portion of the male member is ground.
Preferably, the unthreaded forward portion of the male coupling portion taper at an angle xcex11 with respect to the axis B, the unthreaded forward portion of the female coupling portion taper at an angle xcex12 with respect to the axis C, the angle xcex11 being equal to the angle xcex12.
Typically, the angles xcex11 and xcex12 are in the range of 2.5xc2x0 to 3.5xc2x0.
Further typically, the angles xcex11 and xcex12 are 3xc2x0.
Optionally, the angle xcex11 is greater than the angle xcex12 by 0.25xc2x0.
In accordance with a preferred embodiment, the thread portion of the male member and the thread portion of the female member are a single lead threads.